262 



ANIMAL MECHANICS. 



probably did not correspond to that described by Meyer and termed by 

 him miliMrisch, and this again certainly does not correspond with the 

 bequeme-hcdtung of Braune and Fischer. 



In Fig. 147 three figures of a man are represented (a) bending backwards, 

 (b) standing erect, and (c) bending forwards. In a and c the centre of 

 gravity actually falls outside the body, and it will readily be understood how 

 the slightest movement in b, either forwards or backwards, will shift the 

 position of the centre in relation to the joints. 



The following points may be readily ascertained by the aid of the apparatus 

 for ascertaining the position of the centre of gravity mentioned on p. 259. 

 Where the centre plumbs over the ankle-joint, or lies behind it, the body is 

 held uncomfortably erect, and there is a feeling that it would easily be caused 

 to fall backwards. In the most comfortable position 

 the centre plumbs in front of the ankle, but when 

 it is caused to fall over, or nearly over, the ball of 

 the great toe, as in the position of attention, there 

 is a feeling of strain, and the posture cannot be 

 maintained long without great discomfort. On this 

 account soldiers are not kept long at attention by 

 officers of experience ; indeed, it is very doubtful 

 whether this position should be retained at all, for 

 it is questionable whether a smart appearance, and 

 the gaming of half a second in commencing to march, 

 compensate for the waste of considerable muscular 

 activity. 



There is no erect posture of the body which can 

 be long maintained without exhaustion. 1 If we are 

 called upon to stand for some length of time, we in- 

 stinctively change our posture from time to time, 

 throwing the strain first on one set of muscles and 

 ligaments and then upon another. The position of the 

 centre of gravity changes with any deformation of 

 the figure. Thus, a protuberant belly, either caused 

 j^y p re or nanc y or b v excessive development of fat, causes 

 , / , * ^ -\ i_ 



^ ne cen ^ re * move forwards, so that the obese or 



plumbs with centre of pregnant person has to hold his or her head and 

 gravity. The centres shoulders well back, in order that it may plumb 

 of rotation of ankle, w ithi n the area of ground covered by the feet. A 

 behind ' this plumb! burden on the back, on the contrary, causes the 

 li ne> centre common to the burden and the individual 



carrying it, to move backwards, so that the bearer 



has to bend forwards in order that the centre may fall plumb with the 

 feet. 



Viewing the body as a rigid body, we shall find that its stability will 

 depend upon its height and the area of its underpropping (see Fig. 149). If 

 we imagine a force (push) acting through the centre of gravity in the direc- 

 tion of the line ac, it will, if great enough, cause the body to fall over the 

 toes at the point /. In so doing, it will overcome the force of gravity 

 acting downwards at the distance fd. 



The question is really one of the moment around the point /. At the 

 instant the overturning is just about to commence, the moments around / will 



1 In the horse, the weight of the animal is largely supported by what are termed 

 "check ligaments," found both in the fore- and hind-legs. The animal can on this 

 account remain standing for a considerable time without fatigue, and can sleep in the 

 standing position (F. Smith). 



FIG. 148. A soldier in 

 the erect posture. The 

 black vertical line 



